Here are those photos, with more context. I started out through the woods from Ringe Rd, up a bit of the "Fitchburg Reservoir No Trespassing Rd", into the woods and up one branch of the Falulah. Passed this wall:

Then I headed up the brook and saw that lovely little quartz on boulder (here) right next to the brook. It is a ravine of sorts. A moment later there was a buried mound. So far gone, I would have missed it a year ago. Now I spot it and notice other faint traces.

A pile:

A crescent, well buried, next to the brook:

Then I cross the brook below the stone bridge, use the old road for a while, then cut back down into the woods again only to come up on the back side of a site I know well at one of the headwaters of Falulah Brook. Sure enough, there were some large things I had not seen before:

And:

And here was something of such dimension that I would have taken it for house foundation:

And below in a new ravine, a faint new brook started, and was this a dam and a mill? Or what is this rectangular structure coming out from the wall?

And what was up with these large mounds in what might have been a millpond? Well, at least in a brook floodplain:

Here is a one:

And another, with quartz:

closer:

And here was another:

With it's quartz (on the right in previous picture):

The main brook, where I came in, flows off
in a different south-facing valley. On this one, on this side of the
hill, there was not much of a brook. I followed the ravine downhill,
past rock piles built into outcrops that reminded me of the day before,

past places oozing water, into a boulder filled amphitheater where every
rock seemed suspect. The boulder fields might have been ruins, the
little niches had to be real.

It was like what I saw in Franklin but not identical. Similar enough to make me think it was the same people. But the extra age I felt about Franklin, translates into a suspicion that those same old people were pushed out of Franklin - a coastal area - back into the rocky foothills of Fitchburg. According to this narrative, they lasted longer, until a later date, in Fitchburg.